Hi JustAMum. Sorry this is long but I figured it was better to paint an accurate picture. I'm not saying our way is right or wrong but here's how it works for us...
My daughter pays me AUD$1,000 a month for looking after my 2 1/2 year old GD 3 full days and 2 half days a week which works out to about 60% of what she'd pay for formal childcare, but it does almost cover my mortgage. At nights and on weekends I build musical instruments when I have the energy left after a long day and do some computer work for a friend's company. It's a struggle financially and there's no money for kicking up my heels but it's not forever. Once she starts school in another couple of years I'll pick her up in the afternoons so most of my days will be mine again and I can get my finances back on track.
I pay for anything needed while GD is with me, so nappies, wipes, food, medicines etc. On the 2 half days GD goes to a "proper" childcare centre (which the daughter pays for) and I pay for petrol to pick her up (a 50Km round trip but not as bad as it seems as I live in a semi-rural area and most of it a 100Km/h speed limit). Our government also provides a small payment for out of pocket expenses for "informal" child care arrangements. I think it's 50c an hour for up to 40 hours a week, but I just sign a heap of the forms and let my daughter claim it back every few months. Of course I buy treats and odd bits and pieces of clothing if I see anything on special, but every now and then my daughter will either give me a few dollars extra or maybe take me out for a meal to even things up.
When my daughter and/or son in law are on holidays or it's a public holiday they have her, so I see that as "holiday pay". If I have a specialist appointment (I have a managed heart condition) one of them takes a half day from their annual leave so once again I see that as "sick pay". 
I know it's costing me money overall but what price do you put on being a big part of a child's life? When my daughter was that age I was working as a sales rep so I really only saw the kids on weekends and to tuck them in at night. Probably more importantly to me I never knew my grandfathers and my grandmothers were loving but matronly hands-off women who died by the time I was a teenager so my memories of them are mainly Mothers' Days, Christmas Days, lunches where you had to be on your best behaviour and by the time I was a teenager they really didn't factor in my life and before I knew it they were gone. I kind of like the idea that my GD will be have fond memories of her loving, fun, quirky Poppa when I've gone.